Mary Anderson, the mother of Dominick Anderson who allegedly beat a police officer with an elephant tusk this morning in Hamilton Heights. Photo: David McGlynn

A Hamilton Heights man, fearing he was under a “voodoo” spell, badly injured a cop this morning, beating him with a plastic elephant tusk, officials said.

The injured officer was trying to break up a domestic brawl between 26-year-old Dominick Anderson and his grandmother inside a building on St. Nicholas Avenue and West 145th Street at 8:10 a.m., police said.

A bystander flagged down officers and led them inside, Anderson’s family said.

“My son has psychiatric problems, he thinks my mother is doing the voodoo on him,” said his mom Mary Anderson.

The distraught mother couldn’t believe what she had just seen: “Oh my God, oh my God.”

The officers went inside and tried to pry Dominick Anderson off 62-year-old Beverly Holmes, police and family said.